The researchers compared different types of egg yolk from birds like hens, geese, and quails to see how well they protect dog semen when it's frozen. They found that using quail egg yolk resulted in higher sperm movement and speed after thawing compared to hen or goose egg yolk. However, there were no big differences in sperm health between the different egg yolk types. This suggests that using goose or quail egg yolk could be a good option for preserving dog semen.